Child seat base



FIG. 1 is a perspective view of a child seat base, showing my design;

FIG. 2 is a perspective view thereof supporting a child seat shown in broken lines, the child seat being for illustrative purposes only and forms no part of the claimed design;

FIG. 3 is a left side elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a front side view thereof; and,

FIG. 7 is a back side view thereof. 

I claim the ornamental design for child seat base, as shown and described. 